Which of the following grammars is (are) ambiguous? (A) S → SS | aSb | bSa | λ (B) S → aSbS | bSaS | λ (C) S → aAB, A → bBb, B → A | λ, where λ denotes the empty string

1. A(A) and (C) only
2. B(B) only
3. C(B) and (C) only
4. D(A) and (B) only

Pick an option to check yourself, or open the answer below.

Show answer & explanation

Correct answer: A. (A) and (C) only

Explanation

In A, S → SS can split a string in several ways. In C, abbbb can be derived with the inner B or the outer B producing the second bb, giving two parse trees.

Note: no option is fully correct; the official key (A) is shown. Grammar B is also ambiguous (abab has two parse trees), so strictly all three are ambiguous; no option says so. The official key is A.